DESCRIPTION (Adapted from Applicant's Abstract: Most partial epilepsies are acquired through brain injury and subsequent development of hyperexcitability by a process of epileptogenesis. Pathologically, hippocampal sclerosis is frequently found and the experimental studies suggest that selective hippocampal damage can lead to abnormal hyperexcitability of epilepsy. This epileptogenic process is likely mediated by excitatory amino acid receptor (EAA-R) mechanisms. EAA-R activation can initiate a cascade of cellular-molecular processes, including the induction of a host of immediate-early genes (IEGs), such as c-fos, c-jun, and NGF-A/B. However, it is controversial whether these IEG inductions simply represent epiphenomena. Our overall hypothesis is that a set of IEGs as transcription factors, regulate the expression of many target genes that underlie the long-lasting hyperexcitability of epilepsy. Establishing the causal role of IEGs in neuronal damage and development of hyperexcitability would be a critical first step toward understanding the mechanism of epileptogenesis. Organotypic culture of hippocampus combines the advantages of long-term survival, preservation of intrinsic network capable of seizures in vitro, and easy accessibility, providing a versatile experimental model for mechanistic studies. Preliminary studies show that IEG immunoreactivity and excitotoxic neuronal damage can be blocked by antisense oligodeoxynucleotides, confirming the usefulness of this culture system and the feasibility of the proposal. The proposal addresses three specific aims: (1) To examine the temporal and anatomic patterns of hippocampal neuronal injury and IEG expression following electrically induced seizures in the organotypic culture; (2) to verify whether antisense oligodeoxynucleotides can selectively block the IEG expression; and (3) to determine if the neuronal injury and hyperexcitability can be prevented by these specific antisense sequences. The IEG and mRNAs and proteins will be assayed by in situ hybridization, immunohistochemistry, and Western blot. Propidium iodide fluorescence, histology and in vitro extracellular electrophysiology will be used to measure neuronal injury, damage and hyperexcitability. The results from this proposal will establish whether or not these IEGs have a causal role in epileptogenesis, providing a vital insight into the molecular mechanisms underlying CNS responses to seizures and neuronal injury. Novel strategies can be devised to prevent development of epilepsy once brain injury occurs. Furthermore, knowledge gained here on excitotoxic mechanisms may lead to formulation of new therapeutic strategies in head trauma or strokes.